1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus. More particularly, the present invention relates to an electrophotographic image forming apparatus having a contamination prevention member which prevents a laser scanning unit from becoming contaminated.
2. Description of the Related Art
Typically, an electrophotographic image forming apparatus, such as a laser beam printer, forms an image as a visible image on a sheet of paper in response to an image signal applied to the electrophotographic image forming apparatus.
The developing unit to which an image signal is applied, attaches toner to an electrostatic latent image formed on a photosensitive medium using a light scanning unit so that the visible image is formed. When the visible image is transferred and fused onto the sheet of paper, the image signal is formed onto the sheet of paper as a desired visible image.
The laser scanning unit forms an electrostatic latent image having a predetermined potential by radiating a laser beam on the surface of the photosensitive medium in response to the image signal. The laser scanning unit typically includes a plurality of optical systems such as a laser diode for generating a laser beam, a collimating lens, a polygon mirror and an f-θ lens.
The laser beam generated by the laser diode passes through the plurality of optical systems, and the electrostatic latent image is formed on the photosensitive medium. However, when the image forming apparatus is transferred to another place, dust, or in particular, toner powder, can contaminate the optical systems. Dust may enter the laser scanning unit during use, get onto portions of the embedded optical systems, and the laser beam irradiated from the laser diode can be disturbed by the dust, such that it does not pass through those portions of the optical systems and a desired electrostatic latent image is not formed on the photosensitive medium.
In order to solve this problem, according to Japanese Patent Publication No. 2001-117035, dust-tight glass is provided where the laser beam of the laser scanning unit is emitted so that dust, such as toner powder does not enter the laser scanning unit.
However, when dust gets onto the dust-tight glass, such as toner powder, the laser beam does not pass through that portion, and the desired electrostatic latent image may not be formed on the photosensitive medium.
In addition, a cleaning unit to which a brush is attached, is installed where the laser beam of the laser scanning unit is emitted so that when dust gets onto where the laser beam of the laser scanning unit is emitted, dust is removed by moving the cleaning unit.
In particular, due to vibration or shock occurring when the toner powder is mixed with toner or foreign substances during a test process and a product whose test is completed after manufacturing is delivered from a factory to a customer, the product may be shaken and toner powder may get onto where the laser beam of the laser scanning unit is emitted. If the customer uses the product in this state, the laser beam does not pass through the portions with the toner powder thereon, and the electrostatic latent image is not formed on the photosensitive medium. As such, image quality failures occur, and unnecessary repair services are required.